A large variety of devices exist for the generation and/or input of electrical signals to electrically-controlled machines in response to the application of an input force. On such type of electrical signal generator employs one or more piezoelectric elements for generating electrical signals in response to respective manual actuation. such piezoelectric signal generators are used in a variety of applications requiring durability at a reasonable cost, as for instance to provide the input device for various keyless or coded entry systems as for automobiles, offices, residences, etc. More specifically, U.S. Pat. No. 4,190,785 to Kompanek for "Pressure Sensitive Signal Generator Using Piezoelectric Coating" discloses a signal generator employing a piezoelectric material deposited on a substrate as a slurry and subsequently cured. Further, a signal generator of such construction is disclosed as the input generator for an entry system associated with an automobile in U.S. Pat. No. 4,206,491 for "Entry System" by Ligman et al.
The piezoelectric signal generator disclosed in the two aforementioned patents employs a coating of piezoelectric ceramic material as its pressure responsive electrical signal generator. The piezoelectric ceramic is applied to a metallic substrate in the form of a slurry and is subsequently cured to provide an adherent coating. A plurality of electrodes are bonded to the piezoelectric coating at various locations on its surface opposite to the surface bonded to the substrate. The application of manual force to the substrate in the region of one of the electrodes serves to deform the piezoelectric material thereat to generate an electrical signal at the electrode.
While such slurry-deposited piezoelectric signal generators have been effective electrical signal sources, they also have had certain limitations. For instance, because in the signal generator embodiments illustrated in the two aforementioned patents the piezoelectric ceramic is applied as a continuous coating, it is somewhat difficult to provide a plurality of discrete signal generating locations due to the effects of electrical cross-talk. Further still, the slurry-deposited piezoelectric ceramic coating characteristically requires a significant pressure of deformation to provide a particular voltage output, and may be adversely affected by high moisture levels.
On the other hand, other signal generating devices such as the "Manual Electronic Keyboard" of U.S. Pat. No. 3,464,531 to Herr et al have existed for the provision of electrical signals in response to manual actuation of discrete piezoelectric crystals. Such configuration has the advantage that the crystals may be capable of providing a stronger electrical signal than a slurry-deposited piezoelectric ceramic and it avoids the problem of cross-talk. However, the actuating mechanism of the U.S. Pat. No. 3,464,531 is relatively complex and bulky, and is subject to fatigue resulting from repeated displacement of the actuator.
Still further, it may be desirable in certain instances to provide illumination for the signal generating devices. One such example is seen in the aforementioned U.S. Pat. No. 4,206,491 wherein a bulb mounted near the signal generator provides illumination when the generator is first operated. That arrangement requires, a bulb separate from the generator and may not provide uniform illumination. Another example is seen in U.S. Pat. No. 4,060,703 to Everett for "Keyboard Switch Assembly With Tactile Feedback Having Illuminated Laminated Layers Including Opaque or Transparent Conductive Layer" which provides a flexible electroluminescent panel in a sandwich type computer keyboard with keys characterized by tactility. However, that type of switch assembly is relatively bulky in order to accommodate the required actuator displacement, which displacement also tends to limit the service life of the switch. Moreover, such switch assembly is more suited for the relatively "friendly" environment of computer keyboard usage than for the environment of an entry system which may be exposed to darkness and the elements.
Although a variety of signal generating switches have possessed one or more of the qualities hereinbefore discussed, none are available which combine most or all of those features so as to be especially suited for providing input signals for an entry system.